$5st + 2su - s + 8 = 9t - 9$ Solve for $s$.
Answer: Combine constant terms on the right. $5st + 2su - s + {8} = 9t - {9}$ $5st + 2su - s = 9t - {17}$ Notice that all the terms on the left-hand side of the equation have $s$ in them. $5{s}t + 2{s}u - 1{s} = 9t - 17$ Factor out the $s$ ${s} \cdot \left( 5t + 2u - 1 \right) = 9t - 17$ Isolate the $s$ $s \cdot \left( {5t + 2u - 1} \right) = 9t - 17$ $s = \dfrac{ 9t - 17 }{ {5t + 2u - 1} }$